A number of implantable blood pumps presently are under development for application as either artificial hearts or cardiac assist devices. Both centrifugal and axial-flow pumps can be utilized in blood pumps.
A typical blood pump includes a pump housing that defines an inflow port, an outflow port, a pumping chamber, an impeller mechanism mounted within the pumping chamber, an electric motor rotor coupled to the impeller mechanism for blood pumping action, and an electric motor stator that actuates the rotor by an electromagnetic force. The impeller mechanism can be mechanically coupled to the rotor via a transmission shaft as in, for example, a centrifugal-flow type pump. Alternatively, the impeller mechanism or blades can be attached directly to the rotor as in, for example, an axial-flow pump.
The motor stator typically includes three or more groups of windings. Each winding group is formed from a conductive wire wound around a stack of metallic stampings. The motor rotor contains a permanent magnet. In effect, the stator and rotor together form a brushless dc motor. Typically, the windings are disposed around the rotor. Thus, the stator is annular in shape, forming a ring-like structure that extends around the rotor. In operation, the stator windings are sequentially energized, which creates a rotating magnetic field that drives the rotor about its longitudinal axis. In some cases, the annular stator is positioned in the wall of the pump housing, around the rotor. In axial-flow pump designs, the stator is mounted about the blood flow conduit. In centrifugal-flow pumps, the stator is mounted about a rotor neck that is connected to an impeller mechanism located within the blood flow.
In view of an application of a blood pump in artificial hearts and/or cardiac assist devices, reliability is a critical performance factor. Moreover, blood pumps must ensure that a patient's blood does not become contaminated during use of the pump by blood contacting pump parts that are outside of the blood conduit. As such, pump components are machined to exacting specifications to minimize pump failure and ensure the integrity of the blood pathway. Consequently, pump components are often very expensive. Accordingly, design improvements that can decrease overall consumer cost remain a constant focus of blood pump development.